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A NOVEL ENGINE WITH A SCAVENGING STROKE.

15th January 1924
Page 13
Page 13, 15th January 1924 — A NOVEL ENGINE WITH A SCAVENGING STROKE.
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Each Pair of Cylinders has a Common Combustion Chamber, One Cylinder Compressing Air and the Other a Combustible Mixture.

AN INTERESTING engine, working on the four-stroke cycle but with a scavenging stroke in each cylinder following the exhaust stroke, has recently been described to us, and is illustrated in the accompanying drawing. It is the invention of Mr. P. St. George Kirke, M.A., A.M.I.C.E., A.M.I.M.E., A.M.I.E.E., etc., who is known in connection with gas-fired and waste-heat steam boilers.

The drawing shows the engine as a four-cylindered air-cooled unit having overhead valves, the camshaft running at at one-quarter the speed of the crankshaft, so that it, may operate the two inlet valves per cylinder alternately. The exhaust-valve cams would therefore be doubled. The next most notable departure is that each two cylinders have a common combustion space, the connecting rods of their two pistons operating on a single crank. To an extent the engine is thus similar to the Lucas valveless which was on the market about ten or eleven years ago. But the valveless was a twostroke engine.

The description as given to us is not very clear, but we understand that. the inventor is prepared to run the camshaft at one-half crankshaft speed and then to provide one inlet valve per cylinder or at quarter crankshaft speed, and then to provide two inlet valves per cylinder, in which latter case, on a given suction steeke, air would enter one of a pair of. cylinders and a combustible mixture the other. At the end of the compression stroke the ignition of the combustible mixture in the one chamber would be effected in the usual manner, the resulting rise of temperature and pressure being shared by the air compressed in the second chamber. The next exhaust stroke would expel the gases and the heated air through the exhaust valve common to both cylinders. There are obvious cooling advantages in this arrangement, although the need in these days of low-grade fuels in for the greater retention of heat than in the days of .680 sp. gr. spirit. As the camshaft runs at quarter crankshaft speed the combustion would be arranged to take place first in one cylinder chamber of each throw, and then in the other, thus distributing the temperature evenly' and providing a six-stroke scavenging cycle. The rise of pressure above the compression pressure resulting from the combustion of the charge is approximately halved. It is claimed that the cylinder cooling losses are reduced by the lower mean working temperatures, that as air is the

working fluid, its specific heat is lower at the low working temperatures which appertain to the system, that no valve pockets are required, and that, despite this fact, large valves can be fitted, that the average mixture can be made very weak, although the combustible mixture will be strong enough to ensure quick combustion, that, higher compression ip permissible and yet the parts are kepi cooler, that there is increased volumetric efficiency and that the cost and weigh' of the extra parts are more than counter. balanced by the savings on the cooling system and in the lightening of the bearings, cylinders and reciprocating parts because of the reduction of maximum working pressures.

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